It's been a tumultous year on the London stock market. The blue-chip FTSE 100 index soared to an all-time high of 7,877 in May, but the trend since then has been steadily downward to current levels around 6,750.

But the stock market's overall performance hides a wide disparity in firms' share prices - indeed, some global firms have done very well out of the Brexit-weakened pound while other more domestically-focused companies are suffering from the uncertainty over our future relationship with the EU.

So we asked online investing platform AJ Bell to crunch some numbers and find the ten FTSE 350 stocks (see box below) that rose and fell the most in 2018 - and for its top stock market expert Russ Mould to tell us why.

And remember, just because a stock did well this year, doesn't mean it will next year. In fact, it could mean you've missed the boat.

BEST AND WORST PERFORMING FTSE 350 SHARES OF 2018

Winners

Capital return

Losers

Capital return

1

Ocado

96.2%

335

Playtech

-50.0%

2

Plus500

73.3%

336

Mediclinic

-50.8%

3

Hikma Pharmaceuticals

68.2%

337

Metro Bank

-51.0%

4

Evraz

60.6%

338

AA

-53.5%

5

3i Infrastructure

44.1%

339

Kier

-55.2%

6

Drax

40.0%

340

Capita

-56.5%

7

Jardine Lloyd Thompson

38.4%

341

Spire Healthcare

-59.3%

8

Syncona

30.7%

342

Superdry

-75.4%

9

Pearson

30.1%

343

Indivior

-76.7%

10

QinetiQ

26.3%

344*

Thomas Cook

-77.3%

Source: Sharepad, Refinitiv data. From 1 January to 17 December 2018*Note that six members of FTSE 350 were not in the index in January and do not have a full history for the year: Vivo Energy, Quilter, IntegraFin, Energean Oil & Gas, Avast and Amigo.

BEST PERFORMERS

Russ says: Ocado began to persuade investors that it was indeed really a software and technology play, rather than a marginally-profitable delivery firm.

The company signed more licensing deals for its Ocado Solutions technology and the shares roared higher, helped by a massive 'bear squeeze,' as short-sellers of the stock gave up betting on its shares going down over the summer.

They scrambled to buy stock to cover their short positions, driving the share price to new highs. However, Ocado has drifted lower by quite some way from its highs.

A bid at a 20 per cent premium to the prevailing share price for sector peer John Laing Infrastructure stoked fresh interest in 3i Infrastructure, despite investors' and politicians' concerns over public-private partnership (PPP) infrastructure projects, in the wake of the collapse of Carillion.

WORST PERFORMERS

The biggest share price loser title goes to Carillion, the construction giant and outsourcing firm, which saw its share price go to zero after it was liquidated with debts of £1.5billon in January.

Mediclinic issued the latest in a series of disappointing trading statements in October to cap a dismal year which had already seen the stock relegated from the FTSE 100 index in June.

Mediclinic cited disappointing patient numbers at its Swiss unit Hirslanden, the largest of the company's three operations at just under half of total revenues.

Margins also came under pressure here, thanks to change in Switzerland's regulatory regime.

Meanwhile, trading remains mixed in South Africa and the company's emerging market exposure also worked against it as investors sought safer havens following economic turmoil in Turkey and Argentina (even if the firm has no operations in those specific countries).

Weak first-half results took their toll on roadside assistance provider AA , which was also weighed down by its substantial debts

Weak first-half results took their toll on roadside assistance provider AA, which was also weighed down by its substantial debts, as investors finally lost patience with the firm, whose track record had become increasingly patchy following its stock market listing in 2014.

Bizarrely, the company said that too much demand had prompted a drop in first-half profits.

What it termed as a 'pothole epidemic', the result of the Beast from the East and a cold winter, meant that call-outs reached a 15-year high early in 2018 with the result that AA was forced to pay third-party garages to help customers with an unexpectedly high number of breakdowns.

Stock market analyst: Russ Mould of AJ Bell

Kier and Capita added to the support services sector's tale of woe, which had already seen investors in G4S, Serco, Mitie, Carillion and Interserve take their lumps and Babcock suffer a share price slide as doubts grew about its business model.

Kier announced a shock rights issue in December, to help reassure lenders and suppliers in the wake of Carillion's collapse.

Capita also tapped shareholders for more cash, raising £700 million spring, and the ongoing uncertainties over PFI contracts, pressure from the Government on new outsourcing contract prices and reports of poor progress on specific projects such as military recruitment all weighed on the stock.

Superdry is one of many retailers which will look back on 2018 with no fondness at all.

The Cheltenham firm blamed December's profit warning, its second in three months, on the hot summer but analysts began to wonder whether the brand was past its sell-by date.

Such a debate may be why founder, former boss and major shareholder Julian Dunkerton began to press for a return to the firm, to pile extra pressure on chief executive Euan Sutherland, whose is looking to fix product mix and range issues in the coming year.

Shares in travel agent Thomas Cook hit a six-year low in December after a profit warning prompted analysts to worry about its financial health.

Drug developer Indivior struggled all year in the face of a challenge from rival Dr Reddy's Laboratories to its key drug Suboxone and disappointing sales of its Sublocade injectable drug.

Legal judgements supported the generic challenger which prompted analysts to worry about whether Indivior would need to cut its prices to protect its market share, hitting its profits and therefore its ability to service its debts.

An upbeat trading statement in late December offered some comfort with regard to cost cuts, cash management and the company's plans for both Suboxone and Sublocade, although the share price rally still left investors facing a big loss on the year.

Shares in travel agent Thomas Cook hit a six-year low in December after a profit warning prompted analysts to worry about its financial health.

Earnings disappointed and net debt rose sharply as the company blamed Britain's summer heat wave, even as rivals like TUI and OnTheBeach continued to report healthy profit momentum.